<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        a{
            color:red;
            text-decoration:none;   /*去掉下横线*/
        }
        a:hover{
            color:yellow;
            text-decoration:underline;   /*添加下横线*/
        }
    </style>
</head>
<body>
    <a href="#">百度</a>
</body>
</html>